1. It is impossible to use non-destructive testing (NDT) on composite materials and get useful results.
2. The carbon fiber was wound onto the mandrel without using a criss-cross pattern which results in a weaker pressure vessel.
3. Carbon fiber is a very brittle, not ductile, material. Look at the mess on the track after any Formula 1 crash.
3. You have the differential thermal expansion problems you mentioned as well as differential strain caused by pressure.
4. Carbon fiber suffers its own type of cyclic fatigue and this submersible had been through quite a few cycles.
5. The manufacturer of the acrylic viewport would not certify it for 4,000 meters. It was apparently certified for only 1,500 meters depth.
Other than those few minor things, it was a safe vehicle.
I had not read that Rush bought old carbon fiber at a discount. Is there really an age limit on CF for aircraft usage?
I would add from experience that getting repeatible mix quality with resin materials is very difficult, our resin work in the defense industry was highly variable.
A number of missiles with fiber wound resin shells dis not perform well and had to be culled from the fleet. (Mix was inconsistant for a while, til we learned how to do it.)
“Use By Date”-———Yuppers.